Topological Parametric Amplification of Structured Interface States

Topological photonics provides a robust framework for light manipulation, but integrating coherent parametric processes with spatially structured topological states remains difficult. Here, we demonstrate topological parametric amplification within structured interface states. By constructing a domain wall in a one-dimensional trimer lattice, we create topologically protected interface states distributed across two waveguides. Due to this state distribution, light injected into a single waveguide exhibits continuous spatial beating during propagation, which inherently reduces the spatial overlap among the interacting fields during parametric amplification. We theoretically analyze this impact on parametric amplification and experimentally utilize a platform with high third-order Kerr nonlinearity to realize the parametric process. We achieve a signal gain of 3.5 dB and an idler conversion efficiency of -4.4 dB. These results show that parametric amplification can be sustained within structured topological interface states, providing a pathway to integrate coherent parametric processes into complex topological systems.